Activated magnesium chloride has long been important in the manufacture of high performance catalysts for making polyethylene and polypropylene. It is known in the art that anhydrous magnesium chloride must be activated by mechanical or chemical methods in order to obtain active polymerization catalysts.
Such activation methods typically include:
(i) treatment of MgCl.sub.2 with activating agents such as electron donors; PA1 (ii) ball milling of MgCl.sub.2 and PA1 (iii) reaction of compounds such as Mg organic derivatives with chlorinating agents
There exists a large number of patents concerning use of magnesium chloride in the manufacture of Ziegler-Natta olefin polymerization catalysts. The Ziegler-Natta catalysts seem to include every combination of a transition metal compound and an organometallic compound from groups I to III of the periodic table that will promote olefin polymerization. Magnesium precursors such as dialkyl magnesium, magnesium dialkoxides, alkyl magnesium alkoxides, alkoxy magnesium chloride and the like are being tested and some used extensively for preparing supported Z/N catalysts for polyolefin production. Although magnesium diethoxides (alkoxides) and commercial anhydrous magnesium chloride are the most extensively used solid magnesium precursors, many other magnesium precursors in solid and soluble form have been transformed by various treatments into activated magnesium chloride catalyst supports.
Belgian Patents 785332 and 785333 disclose high yield polymerization catalysts which are prepared from activated MgCl.sub.2, TiCl.sub.4 and internal electron donors, and activated by a mixture of trialkylaluminum and an external electron donor.
Recently compositions of magnesium chloride complexed with tetrahydrofuran (THF) were used in the manufacture of super high activity catalysts for olefin polymerization. In "Polymer Communications, 1988, vol. 29, number 5", P. Sobota et al have studied the reactions between MgCl.sub.2 (THF).sub.2 and TiCl.sub.4 (THF).sub.2 and their use as a component of the Ziegler-Natta catalyst for olefin polymerization.
It is also known in the art that a control of the polymer particle morphology is very important for the plant operability and the transformation of the polymer. Therefore it would be useful to have a polymerization catalyst and process whereby a polymer with a controlled particle size distribution could be produced.
Commercial anhydrous magnesium chloride contains impurities which cannot easily be removed. Further commercially available magnesium chloride is usually crystalline and thus exhibits a low activity. As such, polymer manufacturers often use synthetic routes to MgCl.sub.2 in an attempt to obtain a 100% active MgCl.sub.2. It would be useful, however, to find a process which enables the use of commercial anhydrous magnesium chloride in the preparation of polymerization catalysts.